[samtho]

“Sustainable” as a marketing word was likely chosen to refer primarily to itself, i.e. the production of the fuel itself is sustainable compared to drilling for a known finite resource (crude oil). However, it is ecologically sustainable in that we are using material already making the rounds as opposed to unsequestering carbon sinks only to immediately burn.

There are other benefits, CO2 is not the only greenhouse gas around, and conventional Jet-A releases non-CO2 emissions into the atmosphere. SAF has stricter requirements as to what sort additives are allowed based on each chemicals specific burn profile.